Titanium oxide pigment production



Patented June 13, 1950 UNITED STATES PATENT OFFICE TITANIUM OXIDEPIGMENT PRODUCTION No Drawing. Application July 1, 1946, Serial No.680,846

11 Claims.

This invention relates to the manufacture of titanium oxide pigments andparticularly to the preparation of improved white titanium oxidepigments which exhibit, on X-ray analysis, substantially the difiractionpattern of rutile.

More specifically, the invention pertains to novel methods for producingrutile titanium oxide pigments by conversion of anatase titanium oxideobtained from the hydrolytic precipitation of titanium salt solutions,especially titanium sulfate, seeded with a small amount of a novel typeof nucleating or accelerating agent,

The present application is a continuation-inpart of Our copendingapplication Serial No. 426,248, filed January 9, 1942, now abandoned.

Titanium oxide crystallizes in three different forms, namely, anatase oroctahedrite, brookite and rutile. These forms vary in density and inrefractive index, anatase having a refractive inof 2.53, brookite 2.64,and rutile 2.71. The hiding power of the colorless TiOz pigment willdepend upon its fineness and refractive index, the higher the refractiveindex value, the greater being its potential pigment hiding power. Sincerutile possesses the highest refractive index i? value, its greaterattractiveness as a pigment is apparent.

Anatase and rutile comprise the forms most suitable for use as TiOzpigments. Except those of U. S. Patent 2,253,551 prior commercialtitanium pigments are characteristically in the lower (anatase)modification. This is principally due to the fact that more economicaland commercially attractive methods are available for producing anatasebecause the titanium sulfate solutions from whence they usually resultupon hydrolytic precipitation are more readily prepared through thedissolution of titaniferous ores, such as ilmenite, With sulfuric acidin accordance with well-known methods. Rutile, on the other hand, may beobtained from titanium chloride solutions, but an extremely difiicultand costly type of operation is required in which careful controls mustbe constantly exercised and serious corrosion and other problems areever present. Hence, processes affording production at a reasonable costof a rutile pigment having both proper fineness and acceptable colorenabling their commercial exploitation have not been heretoforeavailable.

When hydrous titanium oxide, such as results from the hydrolysis of atitanium sulfate solution in accordance with, for example, the methodsof U. S. Reissue Patent 18,854, is calcined at temperatures ranging fromabout 900 C.-950 C1,

pigment anatase results. If the calcination is conducted at highertemperatures, above, say, 1000 C., l050 0., 1100" (3;, or higher,conversion of the anatase will take place and rutile will comprise thefinal product. However, such product fails to exhibit the potentiallyhigher hiding power and tinting strength of the higher, rutilemodification because the high temperatures required cause an undesiredsacrifice of particle size, color, and other essential pigmentproperties. Thus, the excessive temperatures which must be employedcause sintering, agglomeration and grit and aggregate formation, induceobjectionable particle size growth, and render the ultimate product toocoarse for maximum hiding power, all of which is reflected in therelatively poor color, brightness, texture, tinting strength and hidingpower exhibited by the final product. Undesirably poor in theseessentials, especially hiding power and color, the product becomes unfitfor many intended use, particularly in coating compositions (paints,enamels, lacquers, etc.) wherein the pigment component must possessthese necessary properties. Obviously, these high temperature conversionprocesses for obtaining rutile from anatase likewise fail to provide anacceptable, commercial form of rutile pigment.

It has been found that these and other disadvantages in prior eiiorts toproduce commercially acceptable pigment rutile can be effectivelyremedied. It is among the salient objects of this invention to providenovel methods and means for achieving that result. Also, it has beenfound that the character of a raw pigment hydrolysate and the ultimatetitanium oxide pigment are greatly influenced by the type ofaccelerating or seeding agent which is employed in their production andby the past history and manner of their preparation. A specific objectof the invention, therefore, is to provide a novel type of nucleatingagent which, when employed in the hydrolysis of a titanium salt,especially titanium sulfate, solution, advantageously imparts to thehydrolysis precipitate certain novel and peculiar characteristics,whereby said precipitate, due to its unusual type, state or condition,readily converts to rutile to produce a high-quality pigment whencalcined at relatively low temperatures, e. g., comparable to thosenormally employed in anatase pigment manufacture. An additional,specific object is to provide a novel method for obtaining a rutilepigment possessing both high hiding power and excellent colorcharacteristics, and such other essential properties as desired tintingstrength, opacity, smallness and uniformity of particle size, texture,brightness, oil absorption, etc. Other objects and advantages will beapparent from the ensuing description of the invention.

These and other objects are attainable in this invention which embodiesthe discovery that when the nucleating or accelerating agent used in thehydrolysis of a titanium salt solution is prepared by treating hydroustitanium oxide under controlled conditions with respect to both basicityand acidity, it will so markedly affect the properties of theprecipitate (especially anatase) from said hydrolysis, that subsequentcalcination thereof at relatively low temperatures and commensurate withthose normally employed in anatase pigment manufacture, inducessubstantially complete conversion of the anatase to rutile and yields acommercially acceptable, high-quality type of rutile pigment.

In a more specific and preferred embodiment, the invention comprisespreparing a seeding agent for titanium sulfate solution hydrolysis, bycombing a relatively pure solution of titanium chloride with an alkalinematerial in such manner that the resulting hydrous titanium oxide willbe successively maintained or ripened under both alkaline and acidicconditions and specific alkaline and acidic normalities.

In description, one practical and preferred adaptation of theinventionwill be alluded to in which out novel seeding agent is first preparedand then used in a titanium sulfate solu tion hydrolysis. Since thepotency of the nuclei is dependent upon the conditions prevailing duringits preparation, reference will be made to those conditions which aremost favorably conducive to the preparation of an optimum form ofaccelerator. It will be understood, however, that the invention is notlimited to such preferred conditions and that variance may be resortedto without departing from its underlying spirit and scope.

In such adaptation, a relatively pure titanium chloride solution (onesubstantially free from iron or other undesired impurities andcontaining not in excess of, say, 125 g. TiOz per liter) is mixed in asuitable primary reaction or mixing vessel with a suitable alkaline orbasic material, preferably sodium hydroxide. ride and alkali solutionsso admixed are maintained at substantially room temperature or below,and preferably at a temperature not exceeding about 50 C. The solutionsare incorporated with each other in such manner and such rates,proportions and liquor concentrations are employed that a substantiallalkaline suspension of hydrous titanium oxide is obtained having anormality ranging from about .2 to .8 N. alkali, and preferably about .4NaOH (determined by titration of the alkali suspension to 7.0 pH andpoint using brom thymol blue indicator with .1 N. H2804 as the titratingagent through dilution of a 25 cc. sample of the suspension to 300-40000.). As a result, the titanium oxide is preliminarily maintained for atleast a relatively short period (usually about l-2 minutes) in aninitial alkaline environment, sufllcient to initiate, promote orincipiently activate the nucleating characteristics thereof. Thealkaline suspension is then converted to an acidic state, preferably toa normality of about .4 N. HCl (or a normality ranging from about .1 to1 N. acid) by titration of the acid suspension with .4 N. HaOH to 7.0 pHend point using brom thymol blue indicator The chloand a 25 cc. sampleof the acid suspension diluted to 300-400 cc. in the titration. Onconversion of the suspension to the acid side, the titanium oxide isaged, ripened or matured for a relatively short period of time, andpreferably at an elevated temperature under the indicated acidconditions. If preferred, conversion from the alkaline to acid side canbe conveniently effected by mixing sufficient additional acidic titaniumchloride solution with the alkaline suspension to provide, preferably, a.5 N. hydrochloric acid suspension. Alternatively and in lieu ofeffecting said conversion in the reaction vessel containing the alkalinesuspension, it may be effected in an associated or secondary mixing orreaction vessel. Whatever the manner in which the the desired TiOzacidification is accomplished, the resulting mixture or suspension ispreferably heated to an elevated temperature, as already indicated,ranging, preferably, from about 75 C. to C. by steam injection orotherwise, and is maintained in such elevated temperature condition fora period of time ranging from about 5 to 50 minutes to inducepeptization thereof (if this is desired) but in any event to afford anessential secondary curing or ripening of the T102 in an acidicenvironment to finally activate, promote or develop its desirednucleating characteristics.

The resulting TiOz seed suspension or peptized sol from the contemplatedcontrolled treatment of hydrous TiOz under both alkaline and acidicconditions can then be employed (in amounts ranging from about 1-5%, andpreferably about 3%, on the T102 basis) directly as an acceleratingagent to promote the hydrolysis of a titanium salt solution, andespecially titanium sulfate. 5 ternatively, it may be cooled (to below60 C. and preferably under 50 C.) prior to use and stored in such cooledcondition until use thereof is desired. Cooling may be convenientlyeffected through the action of a suitable cooling fluid, such as air, orby quenching, through addition of a cooling medium, such as water. Ifavoidance of dilution is desired, the cooling operation may be efiectedby passing the seed suspension in indirect heat exchange relationshipwith the cooling medium.

We have found it desirable and therefore, prior to use, prefer tocoagulate the nuclei, such coagulation being preferably effected bytreating the colloidal T102 sol With suflicient soluble sulfate (such assodium sulfate or sulfuric acid), in accordance with the disclosure ofthe co-pending application of Carl M. Oleson, Serial No. 426,247, filedJanuary 9, 1942, now Patent No. 2,479,637, issued August 23, 1947.

When employed in titanium liquor hydrolysis, our novel nucleating agentwill advantageously provide increased, high yields of an improved formof titanium oxide, and especially anatase, within a relatively shorthydrolysis period, and in addition will provide a form of anatasehydrolysate which, when calcined at relatively low temperatures, e. g.,below substantially 1000 C. and from about 850-975 0., (normallyemployed in anatase pigment manufacture) will yield a substantiallycompletely converted, highquality rutile pigment exhibiting excellenttinting strength, color, hiding power and other essential properties.Prior to calcination we prefer to incorporate in the conventionallywashed and purified hydrolysate small amounts of potassium or sodiumsalts, particularly the sulfates thereof, as contemplated in U. S.Patent 1,892,693. In obtaining an optimum form of pigment which exhibits exceptionally high color and brightness characteristics and otherexceptional pigment values, We prefer to effect the calcination in thepresence of a small amount of a mixture comprising an alkali metal salt,particularly sodium and/or potassium sulfate, and the polyvalent metalcompounds adapted to yield white, insoluble oxides disclosed in thecopending application of James H. Peterson, Serial No. 426,249, filedJanuary 9, 1942 (now U. S. Patent 2,369,246, dated February 13, 1945).After calcination, the product may be subjected to the usual pigmentfinishing treatments, such as wet or dry grinding in pebble, Raymond orother types of mills, following which the pigment is adapted for use inall types of commercial pigment applications.

To a more complete understanding of the invention, the followingspecific examples are given, each being given by Way of illustration butnot in limitation of our invention:

Example I A caustic soda solution, at a concentration of 260 g. perliter NaOH, is mixed in a corrosionresistant reaction vessel with atitanium chloride solution, containing 60 g. per liter T102 and about 98g. per liter of active HCl, until an alkaline TiOz suspension, at anormality of about .8 NaOI-I, is obtained. Sufficient hydrochloric acid,at a 25% strength, is then incorporated in said alkaline suspension aswill convert the same to an acidic suspension with a normality of about.5 l-lCl. This acid TiOz suspension is then heated to about 85 C. and isheld at that temperature for about 25 minutes to effect a final curingof the TiOz and peptization to a colloidal sol. A quantity, based on theT102 present, of said sol when used in the hydrolysis (through boilingfor 3 hours) of a titanium sulfate solution obtained from the sulfuricacid dissolution of ilmenite and containing about 250 g. T102 per liter,with an F. A. value of 70, resulted in a yield in excess of 95% anatasetitanium oxide. This hydrolysate, after being filtered, acid-washed andcalcined for 30 minutes at a temperature of about 950 C., while mixedwith a small amount of sodium sulfate (5% on the T102 basis) convertssubstantially completely to rutile to yield a high-quality pigmentexhibiting increased hiding power and exceptionally high tintingstrength and color.

Example II A caustic soda solution is made up to a concentration of 271g./l. NaOH in a large mixing tank. A titaniun'i chloride solutioncontaining 50 g./l. TiOz and about 82 g./l. of active HCl is stored in anearby tank. The titanium chloride solution is added to the caustic sodasolution until the mixture reaches about 1.0 NaOH, following wh' hfurther additions of chloride solution are continued to provide a finalTiOz concentration of 40 g./l. TiOz at an acid normality of about .45N.HC1. This acidic Suspensionis then heated to about 98 C. and held atthis temperature for about 20 minutes, during which further conditioningor activation of the T102 results and a peptized, colloidal TiOz sol isobtained. The sol is then simultaneously cooled and coagulated by addinga cold solution of caustic soda thereto, sufficient to provide about 7.0pH and as contemplated in the aforesaid Carl M. Olson application.Chlorides present are then removed from the coagulated sol by washing ina filter press, after which the seeding material is ready for use. Uponemploying a 4% quantity (based on the TiOz present) of the recoverednucleating agent in the hydrolysis, by boiling for 3 hours of a titaniumsulfate solution, obtained from sulfuric acid dissolution of atitaniferous ore and containing about 190 g. TiOz per liter, a 96% yieldof precipitated anatase results. This hydrolysate, after the usualwashing and purification treatments, yields on calcination at atemperature of about 930 C. for a period of about 30 minutes in thepresence of a .2% amount of potassium sulfate (on the T102 basis), asubstantially completely converted rutile pigment greatly increased inhiding power and of exceptionally high tinting strength and color,greatly superior to commercial anatase pigments.

Example III One liter of caustic soda, containing 240 g. NaOI-I, isadded to 1. liter. of titanium chloride solution, containing 100 g. T102and 182.5 g. HCl, over a 5minute period, to give a suspension oftitanium oxygen compound in about .5 N. NaOH. This suspension is allowedto age in the alkaline environment for about 3 minutes, after which 350cc. of titanium chloride, corresponding in concentration to the originalsolution, is then added to the suspension. The acidic suspension is thenheated to C. and held at this temper ature for about 15 minutes,following which it is cooled and coagulation is effected as set out inthe next preceding example. The use of 3% of this seeding agent in thehydrolysis of titanium sulfate solution at. a concentration of 220 g./l.TiO2 yields a hydrolysate which, after calcination at about 935 C.,exhibits substantially the rutile diffraction pattern on X-ray analysisand possesses excellent pigment properties, especially improved hidingpower, tinting strength and. color.

Example IV A solution of titanium chloride, containin g./l. TiOz and182.5 g./l. active H01, and a caustic soda solution containing 249 g./l.NaOI-l are simultaneously added to a suitable mixing vessel, the ratesof addition being so adjusted that an alkaline suspension, containingabout .6 N. NaOi-I, results. This mixture or suspension is then added toa relatively pure titanium chloride solution, similar in composition tothat used initially in effecting the simultaneous strike. The amounts oftitanium chloride solution and cans-- tic solution used in thesimultaneous strike as well as the titanium chloride solution into whichthe simultaneous strike mixture is introduced are adjusted to provide afinal suspension containing 41 g./l. TiOz and .5 N. H01. The resultingacid suspension is then heated to 90 C. and held at this temperature forabout 15 minutes, following which cooling and coagulation of thepeptized material is effected in the manner set forth in Example II. Theuse of this seed at a 5% level in the hydrolysis of titanium sulfatesolution having a 210 g./l. T102 concentration and an F. A. (free acid)value of 70, yields a product which readily converts to rutile at about930 C. and exhibits high hiding power, tinting strength and colorvalues.

Example V A solution of titanium. chloride containing 100 g./1. T102 and182.5 g./l. active HCl and a caustic soda solution containing 216 g./l.NaOH are simultaneously added to a mixing vessel at adjusted rates togive an alkaline suspension containing .2 N. NaOH. To this alkalinesuspension is then added sufiicient HCl to give about .52 N. HCl. Thisacid suspension is then heated to 70 C. and held at this temperature forabout 100 minutes. Cooling and coagulation is effected as in Example IV.The use of this seeding agent at the level in the hydrolysis of titaniumsulfate solution having a 210 g./l. TiOz concentration and a F. A. (freeacid) value of 70, yields a hydrolysate which upon calcination at about930 C. readily converts to rutile of high pigment quality.

Example VI Orthotitanic acid was precipitated by adding 800 parts byvolume of TiCh solution containing 240 g. T102 per liter to 298 parts byvolume of a solution of NaOH containing 151 g. NaOH per liter to give asuspension containing 57 g. TiOz per liter at pH=6.'7. The precipitatewas washed and was then reslurried in HCl at concentration of 35 gramsTiO2 per liter and 0.35 normal with respect to HCl. The acidifiedsuspension was heated to 80 C. and held at this temperature for 20minutes to efiect peptization. The seed was employed in the hydrolysisof commercial titanium sulfate solution under conditions similar tothose described in Example I, but employing a 5% seed addition (on theT102 basis). The raw pigment obtained converted to rutile at 960 C.which is lower than the conversion temperature of raw pigments preparedby seeding the hydrolysis in accordance with prior art methods. Thefinished rutile pigment obtained by calcinating the hydrolysisprecipitate at 975 C. possessed high tinting strength and excellentcolor.

The tinting strength, color, crystal structure, etc., herein referredto, were determined in accordance with the methods referred to ordescribed in the aforesaid United States patent to James E. Booge No.2,253,551.

The dual-conditioned nucleating agent obtained from this invention, bysubjecting titanium oxide to a plurality of successive treatments undercontrolled conditions with respect to both alkalinity and acidity,consists of an improved form of hydrolysis accelerator having many novelattributes and characteristics lacking in prior TiOz seeding orhydrolysis nucleating agents. It not only has the unique characteristicof so aifecting the properties of an anatase hydrolysate that saidanatase will convent to rutile when calcinated at relatively lowtemperatures, e. g., of the order normally used in anatase pigmentmanufacture, but has many other novel and distinguishing features,particularly in respect to particle size, solubility, rutilecrystallinity, etc. Thus, in contradistinction to the relatively coarsecharacter, diflicultly soluble and dispersible nature of prior agents,it comprises an extremely finely-divided type of material, as is clearlyevidenced from a consideration of its specific surface area values whichrange from about 200-275 square meters and preferably from about 220 toabout 260 square meters per gram of finely-divided material (as measuredby the adsorption method described by Professor J. H. Emmett of JohnsHopkins University in the Analytical Edition of Industrial andEngineering Chemistry, dated January 15, 1941). Having a 30-40%solubility in 50% H2804 at 110 C., the seeding agent is advantageouslyless resistant to such acid solution than prior agents. Thesecharacteristics are very advantageous, the extremely finely-dividedcondition of the agent providing in the hydrolysis a greater number ofnuclei per unit weight with a consequently greater potential forpromoting and accelerating nucleation and hydrolysis. Its finely-dividedcondition increases its solubility characteristics, its rate ofdispersion throughout the solution being nucleated becomesadvantageously increased to reduce greatly the time required foreifective and eificient nucleation and the overall time consumed in thehydrolysis. Also, the finely-divided type of seeding material isexceedingly advantageous in the hydrolysis for effecting a control overthe particle size of the ultimate TiOz pigment, since the smaller andthe greater the number of nuclei the smaller will be the radius of theindividual particles upon hydrolysis completion.

Again, our novel form of nuclei, when subjected to X-ray analysisfollowing heat treatment at temperatures ranging from above 100 C. andup to, say, about 550 C., will reveal a rutile diffraction patternranging from about 10 to 95 or 100%, whereas prior nucleating agents,even though obtained from titanium chloride solutions (U. S. 2,062,133)will not exhibit any rutile diffraction lines when treated and examinedunder comparable conditions. Our optimum form of seed will exhibit thecrystalline form of rutile upon heating at temperatures ranging from300-350 C. The physical disparity in respect to rutile crystallinitybetween a prior seed and one obtained in accordance with this invention,when calcined alone, is demonstrated by the following table, in whichseed A consists of our novel agent, while seed B is of prior art type:

Per Cent When Rutile Calcined Seed 92% (and preferably above 95%) ofthat of MgO,

and hiding power values of 120 or above and preferably above 130.

The values of our novel seeding agent for producing an improved form ofanatase-converted rutile pigment possessing improved pigmentcharacteristics, exceptionally high tinting strength and color orbrightness is particularly illustrated when the above seeds A and B areseparately employed in the hydrolysis of titanium sulfate solutions,using an amount of seed suspension equivalent to 5% on the T102 basis ineach instance to nucleate the titanium sulfate solution which contained215 g. TiOg per liter and 1.? mols H2804 per mol T102. The separatelyseeded liquors were heated gradually to boiling and boiled for a periodof one and a half hours to efiect hydrolysis. The precipitated T102(anatase) formed in such hydrolyses was washed in the usual manner, aciddigested in dilute I-I2SO4, washed, treated with a small amount ofalkali metal salt (0.75% on the T102 basis of a mixture of K2SO4-80% andNa2SO420%), dried at C. and finally calcined. The calcined product waswet ground and dry ground accord- Calcinin n a Per Cent Tinting HidingSeed Textnpaa" Rutile Strength Power Color A 930 95 I90 135 1723Y 950100 195 140 17I2Y The above hiding power values refer to commercialanatase=liic as a standard, and were determined in accordance with thefollowing method involving comparisons with a standard paint appliedover a black and white background. The standard paint comprises anenamel formula containing commercial anatase pigment at a pigmentationof 3 pounds TiOz pe gallon, the hiding power comparison being made withthe rutile pigment sample formulated in the same enamel vehicle to yieldequal paint hiding power. The weight of the anatase required divided bythe weight of rutile in paints of equal hiding power yields the rutilepigment hiding power. For example, if a paint containing 6 g. of rutilehas a hiding power equal to the standard paint containing 8 g. ofanatase, the rutile hiding power equals 8+5 100 or 103 76. The valuesfor color, tinting strength, crystal structure, and absolute reflectanceor brightness were determined in accordance with the 'rnethods describedor referred to in U. S. Patent 2,253,551. The particle size valuesreferred to herein were obtained by a turbidimetric method calibrated bythe ultracentrifuge, the latter being described in U. S. Patent2,952,134. In accordance with such color determining tests, TiOz pigmentto be commercially useful should have a value of 10 or better for actualbrightness before correction for off-tint. Designating a pigment ashaving a color of, say, 1322?? means that the pigment has an intrinsicbrightness of before correction for off-tint and is ofi-tint towards theyellow end of the spectrum to extent of 2 points measured by thearbitrary scale employed in said test. If the pigment is given a colorrating of 8:3Y, it has, in accordance with this scale, an intrinsicbrightness of 11 and is off-tint to the yellow to the extent of 3points.

While we have described our invention as applied to certain specific andpreferred embodiments which advantageously fulfill the objects primarilyenumerated, obviously it is not limited thereto, since the descriptionand examples are merely given by way of illustration and not inlimitation. Hence, while we have enumerated specific processes forobtaining a calcined rutile pigment characterized by improved hightinting strength, hiding power, brightness and color, through conversionof anatase, the indicated preferred modes of obtaining such form ofpigment can be suitably varied. Thus, while the nucleating agent of thisinvention is most outstandingly useful in the hydrolysis of titaniumsulfate solutions and to obtain an improved form of anatase hydrolysatereadily convertible to rutile at usual or normal anatase pigmentcalcination temperatures, it can also be employed, if so desired, in thehydrolysis of other titanium salt solutions, including the chloride,iodide, nitrate, fluoride, oxalate, etc., whether relatively dilute orconcentrated in nature. Any desired concentration of titanium solutionmay be employed in the hydrolysis, solutions having concentrationsranging from about -250 g. T102 per liter being preferred for use.

Although we preferably obtain our novel seeding agent by resorting to aso-called reverse type of strike (in which a titanium chloride solutionis mixed with an alkali solution by adding the former to the latter),other modes of mixing these solutions to obtain our agent can beresorted to. Thus, resort can be had toa so-called direct type of strike(wherein the alkali solution is added to the titanium liquor) or to asimultaneous type of strike (wherein the two solutions are concurrentlyadded to a common mixing or reaction vessel and at controlled rates andconcentrations). Similarly, various combinations of these or othermethods of incorporating the reacting solutions in each other can beused, if desired. It is only essential and critical in the inventionthat the hydrous titanium oxide precipitate resulting from such admixingand which comprises our ultimate nucleating agent shall be subjected,prior to use, to a dual conditioning or ripening treatment under (a)alkaline and (b) acidic conditions, with the alkaline conditioningtreatment preferably occurring first. Since a reverse type of strike ismore suitable and expedient for accomplishing this dual conditioningeffect, it is preferred for use, because by striking the titaniumchloride solution into the alkali, an initial aging of the T102 in apredominantly alkaline environment or condition necessarily takes place,following which the strike continues (through further titanium liquoradditions) until conversion of the mixture to the acid side or normalityresults. If desired, the titanium liquor addition may be interrupted andconditioning of the hydrous T102 under alkaline conditions can beadvantageously prolonged for any desired extent, after whichinterruption further additions of the titanium liquor or monobasic acidcan be effected and continued until conversion of the TiOz suspension tothe acid state materializes. It is evident that preliminary treatment ofthe T102 under alkaline conditions can also be effected in simultaneousand direct types of strikes by controlling the concentrations, rates andmanner in which the solutions are mixed. Thus, where the alkali is addedto an excess of titanium solution, the addition is so regulated andcontrolled that formation will take place of alkaline zones or pocketswithin the resulting mixture, such zones being sufiicient in extent andduration that the precipitated TiOz flocs formed during the mixingoperation will necessarily be surrounded by and maintained in asubstantial alkaline environment and for the period required to effectthe desired aging or curing in such environment. This can be effected,for instance, by conducting the mixing operation in such manner that aquick and rapid alkali addition to the titanium solution is had withaccompanying relatively poor or weak circulation or agitation of themixed solution. The existence and extent in terms of time during whichsuch alkaline zones prevail within the mixture are readily ascertainableby employing an indicator such as phenolphthalein in the solutionmixture. Alternatively, one may, if desired, strike directly under acidconditions, convert the strike liquor to the alkaline side, and thenreconvert back to and mature under the required final acidicconditioning.

As indicated, We prefer to precipitate the hydrous T102 used inpreparing our seed in an alkaline environment. While the manner in whichthe titanium and alkali solutions is mixed is noncritical and a reversetype of strike comprises a preferred mode for producing a TiOz hydrateuseful herein, it is essential and critical to the invention, as noted,that the precipitate be matured, aged, conditioned, cured or ripened forat least a relatively short period of time during some stage of thenuclei preparation operation under controlled conditions with respect toalkalinity and acidity. This dual conditioning treatment is convenientlyeffected by subjecting the precipitate to successive treatments,initially under controlled alkaline conditions and subsequently undercontrolled acid conditions. The alkaline environment under which suchprecipitate is treated should be at least substantially equal to thatshown by phenolphthalein as an indicator, and ranges from in excess ofabout .05 N. alkali to about 2.5 N. or higher, with a range of fromabout .1 to 1.0 N. NaOH being optimum and preferred. The duration orextent of such alkaline treatment, though variable and somewhatdependent upon the prevailing temperatures, concentrations andnormalities used, must be for a period of at least .25 minutes and mayrange up to 30 minutes or longer. A preferred alkali aging orconditioning time ranges from about 1 to 5 minutes at the indicated,preferred normalities. The alkali-conditioned TiOz can then be subjectedto ripening or maturing under acidic conditions and at normalitiesranging from in excess of about .05 N. acid up to about 2.5 N. acid orhigher, with a range of from about .1 to 1. N. HCl being preferredbecause optimum. The length of time the T102 is cured under acidconditions is also variable and depends upon the prevailing acidity, theconcentrations, and the temperatures used. Preferably, such conditionsof acid cure are employed as will induce p-eptization of the T102 undertreatment. Conveniently, this can be accomplished through use of arelatively strong, acidic peptizing agent which is free from sulfate orother polyvalent ions, such as, preferably, an acidic titanium chloridesolution, or monobasic acids generally, such as hydrochloric or nitricacids, or of perchloric, perbromic, periodic, hypochloric or hydrobromicacids, etc. In effecting peptization, the TiOz is conveniently suspendedin a dilute solution of the monobasic acid, following which the mixtureis maintained at an elevated temperature (ranging from 50-90 C., andpreferably from 75-90" C.) until peptization occurs and a stabilizedcolloidal TiOz sol results. The amount of peptizing agent used ineffecting curing of the T102 on the acid side is preferably sufficientto provide a concentration ranging from .2 to .5 N., but, if desired,may be at strengths ranging from, say, about .1 to 1 N. The time of acidcuring preferably ranges from to minutes but may vary from 10-60 minutesor from 5 minutes up to 3 hours, depending upon the temperature andconcentrations of the suspension under treatment. Generally, the lowerthe acid concentration and temperature used in the curing operation, thelonger will be the aging time required. With higher temperatures andconcentrations, shorter conditioning periods will be required.

The terms alkalinity or basicity," as herein used, refer to the basiccapacity of the conditioning solution or suspension measured,prelerably, as normality (free alkalinity or amount of action) while theterm acidity refers to the reciprocal of alkalinity, measured by eitherthe degree or amount of acidity present. As already indicated, normalitydeterminations are ascertainable by titration, e. g., alkalinity beingdetermined by titrating the supernatant alkaline liquid with standardacid, and acidity being ascertained by titrating the acidic liquid witha standard caustic solution.

While we usually prefer to employ a sodium hydroxide or caustic sodasolution of relatively concentrated strength, because such type ofsolution is readily available at relatively low cost, more dilute alkalisolutions as Well as other forms of alkaline agents may be substitutedfor or used in conjunction with such preferred agent for reaction withthe titanium salt solution. Any type of soluble base, especially thealkali metal hydroxides or carbonates, such as those of sodium orpotassium, as Well as ammonium hydroxide or carbonate or the alkalineearth metal hydroxides, will be found suitable for use in the invention.Alkaline earth metal hydroxides, particularly those of calcium, barium,magnesium or strontium, are especially desirable for use when titaniumchloride solutions are employed since avoidance is then had of analkaline earth sulfate precipitate which might to some extent hindersubsequent processing of the seeding agent.

As indicated, the concentration of the alkali reagent may be varied overwide limits, the amounts selected for use being such as will provide areasonable TiOz concentration after admixttue with the titanium saltsolution. As stated, the two solutions are mixed in such ratios andamounts that an alkalinity equivalent to from about .05 to 2.0 NaOHresults, under which conditions the titanium precipitates as thehydrate. Preferably, also, an amount and type of alkali is selected aswill provide a titanium hydrate in the reaction mixture ranging inconcentrations from about 10-50 g./l., thereby avoiding relatively thickslurries which would be difficult to agitate, or the procurance ofconcentrations of less than 10 g. TiOz per liter because too thin innature and requiring mixing, reaction or treat ing vessels ofexcessively large size.

The preferred titanium salt solution from which the seeding agent ofthis invention is prepared comprises relatively pure titanium chloride.Other monobasic acid titanium solutions or salts, such as titaniumnitrate, iodide, etc., or mixtures thereof, can be used, if desired.Titanium sulfate solutions may be also used, provided care is taken toremove soluble polyvalent anions from the hydrous TiOz precipitatedtherefrom, the presence of which would inhibit rutile formation. Anionremoval can be conveniently effected, for instance, by repeatedfiltering and washing. The concentration of the titanium solution soemployed is also variable over rather Wide limits, concentrations offrom about 50 to g. TiOz or more per liter being sufficient for mostpractical purposes. Obviously, one may employ a relatively concentratedtitanium salt solution with a, more dilute form of alkali solution toobtain a titanium hydrate suspension in the desired TiOz concentration.As indicated above, the concentration of the starting titanium solutionmay range up to 125 g. T102 per liter with a preferred concentrationcomprising one in relatively dilute form.

The temperature of the solution obtained as a result of mixing thetitanium and alkali solution is preferably that of the room or lower andthe rate of admixture of the titanium solution with the base is suchthat the temperature of the suspension does not exceed, say, about 35C'. In some instances, it may be found desirable to cool the solutionsand the resulting suspension with ice or other type of refrigerantduring the processing.

Conversion of the alkali-conditioned hydrous TiOz suspension to anacidic state and within a preferred range of from about .05 to 1 N. HClmay be effected, as a stated, by mixing therewith suflicient titaniumchloride or other acidic agent until the mixture becomes acid andwithin, say, the indicated preferred normality. Such conversion ispreferably effected by adding a portion of the original titaniumsolution used in preparing the hydrated suspension to the basic oralkaline suspension. The acid normality of the suspension during thesecondary conditioning treatment will be found to bear importantly uponand affect to a considerable degree the potency of the hydrate as anucleating agent.

After the hydrous T102 has been subjected to the dual conditioningtreatment herein contemplated, the resulting sol may be used directly asa nucleating or accelerating agent in the hydrolysis of a titanium saltsolution, and especially titanium sulfate, the amounts of requiredseeding agent for the purpose being relatively small and ranging fromabout 15% or to as high as said amounts being on the T1102 basis. Asalready stated, we prefer to coagulate the peptized sol prior to use,this being conveniently effected by incorporating in said sol a suitablecoagulant, such as a soluble base, and more particularly in accordancewith the disclosure of the said Carl M. Olson application, Ser. No.426,247, filed J anuary 9, 1942. The amount of coagulant so used shouldbe calculated to provide a substantially neutral suspension and thecoagulated product should be washed substantially free of chloride andother ions or electrolysts prior to use as a seed.

The novel accelerating agent of this invention having the desirablecharacteristics of providing on hydrolysis of a titanium sulfatesolution both high TiGn yields and a form of anatase precipitate whichwill convert to rutile at relatively low temperatures and of the orderof those normally employed in anatase pigment manufacture, its use insuch production is obviously preferred. However, it is not limited tosuch uses but, as already indicated, can be employed in the hydrolysisof all types of titanium salt solutions and whether anatase or rutile,or mixtures of both anatase and rutile, are desired as the finalprecipitate 0r pigment.

While calcination temperatures ranging from substantially 850-975 C.,and not exceeding substantially 1000 C., are indicated as preferred foruse in the invention because they afford optimum benefits hereunder,lower or higher temperatures can also be employed. The use of anyparticular temperature or range thereof will largely depend upon thecomposition or inherent nature of the titanium oxide under treatment,the particular pigment properties to be developed and the crystallinityor amount of rutile which it is desired that the finished pigment shallexhibit. In effecting conversions to rutile, we utilize such calcinationtemperatures and times as will promote or effect conversion of at leasta major portion of the 'I'iOz under treatment, and preferably aconversion of at least thereof. In obtaining optimum benefits hereunder,we prefer to utilize such temperatures as will effect from substantially-100% conversions and in excess of substantially conversion. Hence,temperatures ranging to as low as substantially 750 C. and to as high as1050 C. or 1100 C. can be employed where necessary to promote or effectthe pigment development or rutile conversion desired. Accordingly, theterm calcining to develop pigment properties, as used herein and in theappended claims, includes that degree and time of elevated temperaturetreatment to which a raw pigment hydrolysate 0r precipitate is subjectedin order to impart thereto or develop therein such properties asrequisite tinting strength, hiding power, color, oil absorption,crystallinity, 81c.

While the invention has been particularly described as applied to theproduction of straight or unextended forms of titanium oxide pigments,it can be also applied to the production of mixed or extended forms ofT102 pigments, containing varying amounts of other prime pigments suchas ZnS, lithopone, ZnO, leaded ZnO, metallic titanates, etc., of suchinorganic extenders, as barium sulfate, calcium sulfate, calciumcarbonate, magnesium silicates, etc, or mixtures thereof, and which havebeen either precipitated upon 01- coprecipitated or blended with thetitanium oxide during its manufacture, processing or finishing, the T102component of such mixed or extended pigment, which can usually beisolated by known methods, exhibits the pigment values which have beenalready alluded to.

The term titanium oxide or hydrous titanium oxide used herein or in theappended claims is employed in the generic sense and includes theuncalcined T102 precipitates obtained from the neutralization ordilution of a titanium salt solution. It also includes precipitatesobtained through hydrolysis as by the heating of dilute hydrolyzabletitanium salt solutions. These precitates are usually referred to ashydrated titanium oxide, hydrous titanium dioxide, metatitanic acid,orthotitanic acid, and the like. Similarly, the term applies to anyprecipitate obtained from other procedures, such as through thereduction of solutions of sodium pertitanate. Hence, it includes anysuch titanium oxide precipitates having water associated therewith whichmay vary over rather wide limits of hydration and often contain adsorbedanions from the titanium salt solution employed in their production.

We claim as our invention:

1. A process for producing a dual-conditioned, activated T102 nucleatingagent for titanium sulfate solution hydrolysis which comprises mixing amonovalent anion titanium salt solution with sufficient alkali solutionto precipitate all of its titanium content as hydrous titanium oxideinitially maintain the latter for a period of at least one-quarter of aminute as an alkaline suspension, and subsequently maintaining theresulting alkaline treated product in a surrounding acidic environmentranging from .1 to l. N and at an elevated temperature until thenucleating characteristics of said T102 are developed.

2. A process for producing adual-ccnditioned, activated TiOz nucleatingagent for titanium sulfate solution hydrolysis which comprises reactinga titanium chloride solution with a solution of an alkali sufiicient toprecipitate all of its titanium content as hydrous titanium oxide,maintaining the resulting 'liOz precipitate initially and for a periodof at least one-quarter of a minute as an alkaline suspension at anormality ranging from about .05 to 2.5 N. alkali and thereaftermaintaining the alkali-treated product in a surrounding acidicenvironment ranging from about .i to 1.0 N. acid and at an elevatedtemperature ranging from -l00 C. until the nucleating characteristics ofsaid titanium oxide are finally developed.

3. A process for producing a dual-conditioned, activated TiOz nucleatingagent for titanium sulfate solution hydrolysis which comprises reactinga titanium chloride solution with a solution of an alkali to precipitateas hydrous titanium oxide all of the titanium content of said chloridesolution, maintaining the resulting TiOz precipitate initially and for aperiod ranging from about 15 minutes in a surrounding alkalineenvironment ranging from about .1 to 1.0 N. alkali, and thereaftermaintaining the alkali-treated product in a surrounding acidicenvironment ranging from about .1 to 1.0 N. acid and at an elevatedtemperature ranging from 50-100 C. until the nucleating characteristicsof said titanium oxide are finally developed.

4. A process for producing a dual-conditioned, activated TiOz nucleatingagent for titanium sulfa te solution hydrolysis which comprises adding asolution of a titanium chloride to an alkali solution to precipitate allof the titanium content of said chloride solution as hydrous TiOz andmaintain said precipitate initially and for at least onequarter of aminute in an alkaline environment, continuing titanium chloride solutionaddition to said alkali solution until it becomes converted to an acidicstate, the normality of which ranges from .1 to 1 N., and thenmaintaining the resulting acidified hydrous T102 suspension at anelevated temperature until the nucleating characteristics of said TiOzare finally developed.

5. A process for producing a dual-conditioned, activated TiOz nucleatingagent for titanium sulfate solution hydrolysis which comprisesseparately and simultaneously introducing a titanium chloride solutionand an alkali solution into a reaction vessel, employing suchconcentrations of reactants and rates of addition of solutions to saidvessel that all of the titanium content of said chloride solution isprecipitated and the suspension of hydrous precipitated TiOz whichresults is maintained initially, andior a period of at least one-quarterof a minute, in an alkaline TiOz suspension, the normality of whichranges from .1 to 1.0 N. alkali, thereafter converting the alkalisuspension to an acidic suspension having a normality ranging from .1 to1 N., and then maintaining the latter suspension at an elevatedtemperature until the nucleating characteristics of the treated T102product become finally developed.

6. A process for producing a dual-conditioned, activated TiOz nucleatingagent for titanium sulfate solution hydrolysis which comprises adding asolution of a base to an acidic monovalent titanium salt solution toprecipitate all of the titanium content of said titanium salt solutionas hydrous 'IiOz in suspension, continuing addition of said basicsolution until said titanium solution is .05 to 2.5 N. alkali,maintaining said hydrous TiOz precipitate in said alkaline environmentfor a period of at least one-quarter of a minute, thereafter convertingthe alkaline T102 suspension to an acidic TlOz suspension having anormality ranging from .1 to 1 N. by adding suflicient titanium chloridesolution thereto, and then maintaining said acidified TiOz suspension atan elevated temperature until its nucleating characteristics becomefinally developed.

7. A process for producing a dual-conditioned, activated TiOz nucleatingagent for titanium sulfate solution hydrolysis which comprisesprecipitating hydrous titanium oxide in suspension by adding a titaniumchloride solution to a solution of a base until all of the titaniumcontent of said chloride solution is precipitated as hydrous TiO2,thereupon maintaining said TiOz precipitate in an alkaline environmentranging from .1 to 1.0 N. alkali, for a period ranging from onequarterof a minute to thirty minutes, thereafter converting the alkaline TiOzsuspension to an acidic TiOz suspension having an acid normality rangingfrom .1 to 1.0, and then maintaining such acidified TiOz suspension fora period of from about 10-60 minutes at said normality and at atemperature ranging from 50-100 C. until the nucleating properties ofsaid TiOz are finally developed.

8. A process for producing a dual-conditioned, activated TiOz nucleatingagent for titanium sulfate solution hydrolysis which comprisesprecipitating hydrous titanium oxide in suspension by adding a titaniumchloride solution to a solution of a base until all of the titaniumcontent of said chloride solution is precipitated as hydrous TiOz,maintaining the resulting TiOz precipitate initially and for a periodranging from about 1-5 minutes in an alkaline environment ranging fromabout .1 to 1.0 N. alkali, thereafter converting the alkaline TiOzsuspension to an acidic TiOz suspension having a normality ranging from.1 to 1.0 N. acid, and then maintaining said acidic TiOz suspension at atemperature ranging from 50-100 C. for a period ranging from about 10-60minutes to finally develop the nucleating properties of said titaniumoxide.

9. A process for producing a dual-conditioned, activated T102 nucleatingagent for titanium sulfate solution hydrolysis which comprisesprecipitating hydrous titanium oxide in suspension by adding a solutionof titanium tetrachloride to a sodium hydroxide solution and until allof the titanium content of said tetrachloride solution is precipitated,maintaining the resulting precipitate while in suspension and for aperiod of from 1-5 minutes in an alkaline environment ranging from .1 to1.0 N. NaOH, thereafter converting said alkaline suspension to an acidicTiOz suspension having a normality ranging from .1 to 1.0 N. HCl, andthen maintaining said acidified suspension at a temperature ranging from50-100" C. and for a period ranging from about 10-60 minutes to developthe final nucleating characteristics of said titanium oxide.

10. A process for producing a dual-conditioned, activated TiOznucleating agent for titanium sulfate solution hydrolysis, comprisingprecipitating hydrous titanium oxide by adding a titanium tetrachloridesolution to a solution of sodium hydroxide and until all of the titaniumcontent of said tetrachloride solution becomes precipitated, initiallymaintaining the resulting T102 precipitate while in suspension in thealkaline environment of said sodium hydroxide solution having anormality of from .1 to 1.0 N. NaOH for a period of from 1-5 minutes,thereafter peptizing and finally curing said titanium oxide in an acidic17 environment by suspending it in a dilute solution of a monobasic acidat an acid normality of from .2 to .5 N., and maintaining the acidicT102 suspension at a temperature of from '7590 C. for a period of fromabout 15 to 30 minutes and until a stabilized, colloid-a1 TiOz sol isobtained.

11. A process for producing a dual-conditioned, activated TlOznucleating agent for titanium sulfate solution hydrolysis, comprisingseparately and simultaneously introducing a titanium chloride solutionand a sodium hydroxide solution into a reaction vessel, employing suchconcentrations of reactants and rates of addition of solutions theretothat all of the titanium content of said chloride solution isprecipitated as hydrous 'I'iOz, an alkaline TiOz suspension results andthe precipitated hydrous T102 present in said vessel is maintainedtherein for a period of at least onequarter of a minute in an alkalineenvironment at a normality ranging from .1 to 1.0 N. alkali, thereafterintroducing the alkaline TiOz suspension from said vessel into atitanium chloride solution wherein said alkaline suspension becomesconverted to an acidic T102 suspension having a REFERENCES CITED Thefollowing references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,062,133 Kubelka et a1 Nov. 24,1936 2,303,307 Tillman et al. Nov. 24, 1942 FOREIGN PATENTS NumberCountry Date 310,949 Great Britain Dec. 12, 1929 OTHER REFERENCES Weiseret al.: Journal of Physical Chemistry, volume 38 (1934), pages 513-519.

Certificate of Correction Patent No. 2,511,218 June 13, 1950 CARL MARCUSoLsoN Fir AL.

It is hereby certifiect th'at5e 1'"r0rs appearin the printedspecificationof the above numbered patent requiring correction asfollows:

Column 3, line 24, for combing read combining; li-ne61, for the Word andread end; line 74, for HaOH read NaOH; column 4, line-57, for 1947 read1949; column 7, line 15, for 298 parts read 928 parts line 33, forcalcinating read calcining; lines 51 and 52, for convent read concert;same line 52,161 calcinated? read calcined; column 14, line 47, forprecitates read precipitates;

and that the said Letters Patent'should be read with these correctionstherein dieting of the case in the Patent once.- day of September, A. D.1950.

same may conform to the record Signed and sealedthis 12th [SEAL] THOMASF. MURPHY,

Assistant Oommi'ssz'oner of Patents.

1. A PROCESS FOR PRODUCING A DUAL-CONDITIONED, ACTIVATED TIO2 NUCLEATINGAGENT FOR TITANIUM SULFATE SOLUTION HYDROLYSIS WHICH COMPRISES MIXING AMONOVALENT ANION TITANIUM SALT SOLUTION WITH SUFFICIENT ALKALI SOLUTIONTO PRECIPITATE ALL OF ITS TITANIUM CONTENT AS HYDROUS TITANIUM OXIDE ANDINITIALLY MAINTAIN THE LATTER FOR A PERIOD OF AT LEAST ONE-QUARTER OF AMINUTE AS AN ALKALINE SUSPENSION, AND SUBSEQUENTLY MAINTAINING THERESULTING ALKALINE-TREATED PRODUCT IN A SURROUNDING ACIDIC ENVIRONMENTRANGING FROM .1 TO
 1. N AND AT AN ELEVATED TEMPERATURE UNTIL THENUCLEATING CHARACTERISTICS OF SAID TIO2 ARE DEVELOPED.